Thermal expansion of SrZrO3 and BaZrO3 perovskites
Thermal expansion of SrZrO3 and BaZrO3 perovskites
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DOI：
10.1007/bf00200187
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发表时间：
1991-12
影响因子：
1.4
通讯作者：
Yusheng Zhao;D. Weidner
中科院分区：
文献类型：
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作者：
Yusheng Zhao;D. Weidner
SrZrO3和BaZrO3钙钛矿的高温X射线衍射研究已经进行到1200℃。通过Rietveld方法分析衍射图样，以细化晶胞尺寸。观察到斜方Pbnm相的体积热膨胀系数为2.98*10-5K-1，斜方Cmcm相的体积热膨胀系数为3.24*10-5K-1，SrZrO3钙钛矿的四方I4/mcm相的体积热膨胀系数为3.75*10-5K-1，立方Pm3m相的体积热膨胀系数为2.06*10-5K-1分别为BaZrO3钙钛矿。 SrZrO3钙钛矿的线性热膨胀系数对于正交Pbnm相表现出相当大的各向异性αa>αc>αb，这反映了钙钛矿畸变的减少。结果表明，中心对称畸变ABX3钙钛矿的热膨胀可以根据经验表达为[B-X]键长和BX6八面体骨架倾斜角变化的组合。八面体倾斜被认为是钙钛矿中铁弹性结构相变的主要有序参数。在热力学上，倾斜引起的体积变化表示“过剩体积”，相应的热膨胀表示相对于立方钙钛矿原型的较低对称性相的“过度热膨胀”。
High-temperature X-ray diffraction studies of SrZrO3and BaZrO3perovskites have been carried out to 1200° C. The diffraction patterns are analyzed with Rietveld method so as to refine the unit cell dimensions. The volumetric thermal expansion coefficient are observed to be 2.98*10-5K-1for orthorhombicPbnmphase, 3.24*10-5K-1for orthorhombicCmcmphase, 3.75*10-5K-1for tetragonal I4/mcm phase of SrZrO3perovskite, and 2.06*10-5K-1for cubicPm3mphase of BaZrO3perovskite, respectively. The linear thermal expansion coefficients of SrZrO3perovskite show considerable anisotropy of αa>αc>αbfor orthorhombic Pbnm phase, which reflect the decrease of distortion of the perovskite. It is demonstrated that thermal expansion of the centrosymmetrically distorted ABX3perovskite can be empirically expressed as a combination of the changes of [B-X] bond length and tilting angle of BX6octahedral framework. The octahedral tilting is considered to be the primary order parameter for the ferroelastic type of structural phase transitions in perovskite. Thermodynamically, the tilting induced volume change denotes the “excess volume” and the corresponding thermal expansion represents the “excess thermal expansion” for the lower symmetry phase with respect to its prototype of the cubic perovskite.